I. Field of the Invention
The present invention relates to coated metal substrates and more particularly to ferrous articles bearing a phosphate conversion coating thereon.
II. Description of the Prior Art
It is well known that numerous advantages can be achieved by applying a phosphate conversion to a ferrous article or substrate. Two of the most important advantages are the increased adhesion of organic coatings (such as acrylic or epoxy resins or paints) to the substrate, and the increased resistance of the phosphatized substrate (either with or without a subsequent coating) to corrosion, especially at elevated temperatures or humidities. Occasionally steel--itself already adequately susceptible to application of a satisfactory phosphate coating--has been plated with zinc prior to application of the phosphate conversion coating.
Phosphatizing is typically carried out by applying an acid solution of zinc phosphate to a susceptible substrate that has been prepared by surface grinding, acid etching, sandblasting, glass bead blasting, alkaline cleaning or the like. Nickel ion has been included in the phosphatizing solution as an accelerator. The phosphatizing solution can be applied to the prepared surface in a number of different ways, for example, as by immersion, spraying, dipping, wiping, brushing or the like.
Unfortunately, alloys composed of iron, boron, and a rare earth metal such as neodymium, which have particular utility in the magnetics industry, have been found not to be susceptible to conventional methods of phosphatizing. This has reduced the utility of Fe-R-B alloys, which have been subject to some drawbacks in use, such as a less than satisfactory resistance to moisture and corrosion, and poor adhesion of organic coatings intended to protect the alloys from such corrosion.